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Research designed to explore the Grand Plaza at the Cahokia Mounds site, the largest Mississippian-period mound center in the eastern United States, documents that plazas may yield significant information regarding Mississippian manipulation of the landscape and the initial growth of mound centers. Probing and excavation within the Grand Plaza revealed that buried ridge-swale topography, identified through an electromagnetic-conductivity survey, was stripped and then filled by the Cahokians. Excavation also corroborated the presence of deep-pit borrows identified by remote sensing. Based on the ceramics recovered from our excavations, we argue that these earth-moving events were initiated prior to the onset of the Mississippian period (ca. A.D. 1000). Reclamation of the borrowed areas resulted in the formation of the mound-plaza configuration early during the Mississippian period.

Information on depth may be gained through the analysis of geophysical maps, by utilizing soundings, pseudosections, or time-slices, or via the application of downhole measurements. Various methods and techniques were compared at the Biesterfeldt site, a proto-historic earth-lodge village in the Northern Plains, USA. Both traditional and more experimental approaches were used, including ground-penetrating radar time slices and overlay analyses, a resistivity pseudosection, two-and three-dimensional magnetic and resistivity modelling, and downhole tests of magnetic susceptibility, magnetic viscosity, total magnetic field, capacitance and resistivity. A direct-push colour system, measuring the reflection of light over the red-green-blue (RGB) and near-infrared spectrum, provided another useful tool for mapping the depths of archaeological features and stratigraphic layers. Early historic maps of the site show more than 60 earth lodges and an encircling ditch. Current management efforts aim not only to georeference and evaluate the accuracy of these maps, but to determine the state of preservation of the archaeological features. These efforts are complicated by historic cultivation of the southern half of the site. Geophysical tests focused on depth yielded locations and depths for several lodges and the filled ditch as well as small and thin features and layers within them. A buried soil was also identified. Downhole geophysical and direct-push color techniques were particularly helpful for mapping lodges in the plowed portion of the site. These results were confirmed through excavation. Adding geophysical tests focused on depth at Biesterfeldt provided information useful for understanding feature formation, context, and post-depositional processes, and for designing effective at-surface geophysical surveys, planning excavations and site management. These tests highlight the advantages of integrating techniques focused on depth with geophysical area surveys.

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